1. Field of the Invention
This invention relates broadly to surgical instruments. More particularly, this invention relates to loop electrodes which are used in electrocautery probes with a resectoscope.
2. State of the Art
Prior art FIG. 1 shows a typical resectoscope 10 with an electrocautery probe 12. The resectoscope 10 includes a distal guide tube 14 and a proximal handle 16. A telescope 18 extending through the guide tube 14 is provided with a proximal eye piece 20 for viewing the interior of the bladder or other operative site. The cautery probe 12 has a distal electrode 22 which is mounted between a pair of arms 23, 25. The arms 23, 25 are joined at their proximal ends to an electrode lead 27 which is coupled via the handle 16 to a wire 24. The wire, in turn, is coupled to a source of cautery current (not shown). As seen in the prior art FIG. 2, a mounting sleeve 29 is provided on the probe 12 for slideably coupling it to the guide tube 14. The mounting sleeve 29 is typically located at the point where the arms 23, 25 are joined to the electrode lead 27. The handle 16 is provided with the capability of axially sliding the probe 12 and its distally mounted electrode 22 relative to the guide tube 14.
The resection procedure involves applying a cauterizing wattage to the electrode 22 and moving the electrode slowly through or over the prostate or endometrium while viewing the tissue through the scope 18. Thermal energy is applied through the electrode to the prostate or the endometrium so that tissue is excised. The resectoscope and cautery probe are also useful in other procedures for resecting the uterus, ureter, or renal pelvis.
Known electrodes for use in resectoscopes are available in many different shapes and sizes. U.S. Pat. No. 4,917,082 to Grossi et al., for example, discloses several embodiments of a "Resectoscope Electrode" including a coagulating electrode, a knife electrode, a punctate electrode, and a roller electrode, among others. Electrodes for use with resectoscopes are also widely available from Olsen Electrosurgical, Inc., Concord, Calif. They are available as blades, needles, balls, loops, spear tips, flexible wires, semi-circular wires, hooks, spatulas and blunt tips.
The loop electrode 22, which is shown in FIGS. 1 and 2 is the presently preferred type of electrode for prostatic resection because it can be used to cut and to coagulate. The disadvantage of the loop electrode is that in order to make the electrode sharp enough to cut smoothly, it must be made relatively thin with little surface area. The small surface area of the loop electrode compromises its effectiveness as a coagulating tool. Thus, in a prostatic resection procedure, 80% of the time devoted to the procedure is used to coagulate the prostate and stop it from bleeding.
An electrocautery probe solving the problems of the previous probes was disclosed in parent application U.S. Ser. No. 08/425,386 and is shown in FIGS. 3 and 4. The electrocautery probe 112 includes a distal loop electrode 122 mounted between a pair of arms 123, 125, which are joined at their proximal ends to an electrode lead 127, and a mounting sleeve 129 for slideably coupling the probe to the guide tube of a resectoscope. The arms 123, 125 extend parallel to the guide tube and are covered in an insulative material 131, 133 which further extends over an upper portion 131a, 133a of the loop electrode. The loop electrode defines a sharp distal edge 122a, a sharp proximal edge 122b, and a broad lower base surface 122c. A cross section of the electrode is defined by the lower base surface 122c, a distal surface 121a, and a proximal surface 121b. The loop electrode is angled approximately 10.degree. proximally relative to a plane substantially perpendicular to the arms. Tests demonstrated that the electrode is 90% more effective in coagulation than the prior art-loop electrodes. It is believed that the sharp distal and proximal edges aid in cutting and focus cautery current to this effect while the relatively broad base serves to enhance coagulation.
However, it has been found that this probe configuration, when used over a long period of time, is prone to having the insulation 131, 133 around the arms of the probe degrade. Once the insulation degrades, it is technically possible for the electrode to electrically arc to the endoscope through which the probe is inserted.